The Arroyo Formation (Leonardian: Lower Permian) and Its Vertebrate Fossils Everett C. Olson Texas Memorial Museum Bulletin 35 ®1989 by Texas Memorial Museum, The University of Texas at Austin. All rights reserved. Published July 31, 1989 Printed in the United States of America ISSN: 0082-3074-35 Texas Memorial Museum Pub. No. n.s. 2 The Bulletin is an irregularly published series of technical monographs deriving primarily from research done on Texas Memorial Museum collections and projects. - Texas Memorial Museum The University of Texas at Austin - 2400 Trinity - Austin, TX 78705 CONTENTS Abstract 1 Acknowledgments 1 Introduction 2 Materials and Methods 4 General Conditions of Deposition of the Arroyo Formation 6 Terrestrial Sites and Fossils 11 Marine Sites and Fossils 11 Tetrapods 14 Amphibians 14 Lepospondyls 14 Diplocaulus 14 Microsaurs 14 Labyrinthodonts 15 Reptiles 15 Aquatic Vertebrates 15 Class Chondrichthyes 15 Class Osteichthyes 18 Dipnoi 18 Crossopterygii 18 Actinopterygii 18 Invertebrates 22 Discussion and Summary 22 Literature Cited 24 ILLUSTRATIONS Figure Page 1. Distribution of beds of Leonardian age 2 2. Distribution of outcrops of the Clear Fork Group 2 3. Sketch of a typical palaeoniscoid scale 4 4. Distribution by counties of Lueders and Arroyo Limestones 4 5. Map of sites in Haskell and Throckmorton Counties, Texas 6 6. Map of sites in Callahan, Taylor, Shackelford, and Jones Counties, Texas 8 7. Photomicrographs of amphibian specimens 9 8. Photomicrographs of microsaur specimens 10 9. Photomicrographs of fish specimens 12 10. Photomicrographs of amphibian and reptile specimens 13 11. Photomicrographs of fish and invertebrate specimens 16 12. Photomicrographs of scales of palaeoniscoid fishes 17 13. Photomicrographs of scales of palaeoniscoid fishes and Polyptems 19 TABLES Table Page 1. Faunal list of vertebrates known from the Arroyo Formation 3 2. Locations, sediments, and faunas of the terrestrial sites of the southern area 5 3. Sediments and faunas of the marine sites of the southern area 7 The Arroyo Formation (Leonardian: Lower Permian) and Its Vertebrate Fossils Everett C. Olson University of California atLos Angeles ABSTRACT and in making available the facilities and services of the research laboratories on many occasions. Studies of the Arroyo formation from northern Haskell The comments, criticisms, and suggestions of two County south to Runnels County, Texas trace the anonymous referees contributed materially to the and environments from the "clas- changes in organisms final content and form of the paper. Members of sic" terrestrial beds of Baylor and Wilbarger Counties to the Texas Bureau of Economic Geology at The the fully marine sections to the south. Terrestrial depos- at assistance its that contain vertebrate remains have been found only University of Texas Austin provided as far south as Haskell, Texas. Limestones, sampled and in locating and determining the identity of the var- treated by acetic acid, have produced tetrapods to the ious limestones used in the study, activities that level of Abilene, Texas. Among these are the commonest depended heavily upon the appropriate sheets of genera of the Arroyo, including several types of micro- the Geological Atlas of Texas. saurs. Notably absent is the highly terrestrial genus Cap- Drs. Ellis Yochelson and John Pojeta studied torhinus. Above the Lueders the sec- Limestone, Arroyo and analysed the invertebrates of samples from tion in the southern area consists of four marine lime- Sites 13. were stones alternating with varied thicknesses of red mud- 2 and Specimens of palaeoniscids stones, with small increments of sandstones and fine supplied by the USNM for studies of thin sections. conglomerates. The distributions of the limestones and Benjamin Crabtree of UCLA was an assistant in the elastics indicate four major transgressions of the sea, the program and performed extensive studies on with a very irregular coastline during the peaks of trans- the variety of shape-patterns of the scales etched have a wide of gression. The limestones yielded variety from the limestones with particular attention to xenacanthid sharks, various other Chon- fish, including their utility in taxonomy. Specimens of Polypterus drichthyes, and dipnoan and palaeoniscoid Osteichthyes. Special attention is paid to the systematics, distributions, that were used for studies of histological characters and habitats of the fish, with special emphasis upon the of scales and their distribution over the body came use of scale histology in taxonomic studies. from the fish collections of UCLA. The art work for the line drawings was done by ACKNOWLEDGEMENTS Dr. Kathryn Bolles, as was the difficult photomi- crography of whole specimens and transparencies Field work over the 10 year span of this study was used in the figures. Appropriate equipment for immensely enhanced by my wife, Lila Olson, by photomicrography was made available by Dr. Wil- her ability to find obscure fossils in the field and to liam J. Schopf of the Department of Earth and drive back-country in our Jeep as I plotted posi- Space Sciences, UCLA, and by Drs. C. C. Coney tions and ways of access to sites. Drs, Ernest and J. H. McLean of the County Museum of Natu- Lundelius and Wann Langston, Jr., of the Verte- ral History, Los Angeles, California. Research brate Paleontology Laboratory, The University of support was provided by Grants 1638 and 3330 Texas at Austin, were of great help as consultants from the Research Committee, The University of 1 and bounds Wilbarger and Wichita Counties, Tex- as on the north. At the type locality, the formation consists of 66 meters of marine limestone, shale, and lenticular gypsum. In the classic area, the sec- tion is composed of approximately 130 m of red mudstones, shales, sandstones and fine to coarse conglomerate. Throughout most of its length, the lowest beds of the Arroyo Formation rest on the marine lime- stone of the Lueders Formation, the uppermost subdivision of the Albany Group. Overlying the Arroyo beds are the red, clastic, predominantly mudstone deposits of the Vale Formation. The Ar- royo was named by Beede and Waite (1918). The contact between the Arroyo and Vale, as defined by Wrather (1917), lies at the top of the Standpipe Limestone. Because this limestone extends only as far north as the northern edge of Abilene, Texas, precise differentiation of the Arroyo and Vale Figure 1. General distribution of beds of Leonardian age formations is very difficult to the north of that city. (Clyde, Lenders, and Arroyo) in Texas and Oklahoma. Compounding the difficulties of study of the fauna and stratigraphy north of the Standpipe Limestone California at Los Angeles, and in early phases of are the generally flat or rolling topography and an the work by National Science Foundation grant extensive cover of Cretaceous rocks and alluvium. DEB 78998754. INTRODUCTION The Arroyo Formation is the lowest of the three formations that make up the Permian Clear Fork Group (Figures 1 and 2) of north central Texas. The area north of the Salt Fork of the Brazos Riv- er has been extensively studied by vertebrate pale- ontologists (Figure 2), and is the principal source of information about the terrestrial vertebrates that existed during the time of its deposition, aug- mented by data from Oklahoma and Germany. Emphasized in this paper are the Arroyo deposits that lie south of the Salt Fork of the Brazos, here termed the "southern area" in contrast to the better known northern area, here termed the "classic area." A summary of the vertebrate taxa now known from the classic area, together with those which this study has added from the southern area, is given in Table 1. The type section of the Arroyo Formation lies about 240 kilometers south of the classic area, at Los Arroyos, near Ballinger, Runnels County, Figure 2. General distribution of outcrops of the Gear Fork Texas (Figure 2). Outcrops of the Arroyo extend in group and its formations in North Central Texas (modified from Olson and Mead, 1982). In this paper, the area of a to north northeasterly direction from somewhat the the Salt Fork of the Brazos River is termed the "classic area", south of the type locality to the vicinity of the Red that to the south, which is the particular focus of this paper, River, which lies between Texas and Oklahoma, the "southern area". 2 Table 1. Faunal list of vertebrates known from the Arroyo Formation of north central Texas. The family Dissorophidae is consid- ered by some to exclude Trematops, which is then assigned to the family Trematopsidae. The other listed genera then form the fam- ily Dissorophidae and the two families are grouped under suborder (or superfamily) Dissorophoidea. I have not followed this scheme here. The list is conservative, with questionable genera and species omitted. A question mark (?) before a taxon indicates either uncertain identification or, in the case of Cacops, Varanops, and Casea, uncertainty as to whether they are from Arroyo or Vale deposits. An asterisk (*) before a taxon indicates that it was first found in the course of the present study. CLASS CHONDRICHTHYES Subclass Labyrinthodontia Subclass Elasmobranchii Order Temnospondyli Order Pleuracanthodii Family Eryopidae Family Xenacanthidae Eryops megacephalus Cope Onhacanthus platypternus (Cope) Family Trimerorhachidae Orthacanlhus texensis (Cope) Trimerorhachis insignis Cope Xenacanthus luederensis Berman Trimerorhachis mesops Cope Order Selachii Family Dissorophidae Suborder Hybodontoidea Trematops milleri